Multi-layer water-splitting devices

ABSTRACT

Water-splitting devices and methods for manufacturing water-splitting devices or solar cells is disclosed. The method seeks to provide a relatively high-volume, low-cost mass-production method. In one example, the method facilitates simultaneous co-assembly of one or more sub-units and two or more polymer films or sheets to form a water-splitting device. According to another aspect, there is provided an improved water-splitting device. In one example form, there is provided a water-splitting device which includes a first electrode for producing oxygen gas and a second electrode for producing hydrogen gas from water. The first electrode and the second electrode are positioned between a first outer polymer layer and a second outer polymer layer, and at least one spacer layer is positioned between the first outer polymer layer and the second outer polymer layer.

FIELD OF THE INVENTION

The present invention generally relates to water-splitting devices, suchas solar cells, and in one particular aspect to improvements in themanufacture of water-splitting devices.

BACKGROUND OF THE INVENTION

Electrical devices that interact with light are well known. Examplesinclude light-emitting diodes (which emit light), solar cell modules(which harvest light and turn it into electricity), and display screens(which may alter the light that they reflect). Most devices of this typeuse glass in one form or another as the key, transparent substratematerial. This is often problematic however, since glass is typicallyfragile, heavy, expensive, and generally not well-suited to high-volume,low-cost mass-production. For this reason there is increasing interestin using cheaper, transparent polymeric materials in place of glass indevices of this type. Ideally, this will be combined with simple andinexpensive fabrication techniques for the devices themselves, such asthe use of commercial printing processes.

One problem in this respect is to integrate a transparent polymersubstrate into the fabrication of flexible electrical devices. Severalapproaches have been trialled and are being used. A common one(exemplified by the flexible touch-screen disclosed in EP 0348229) is toemploy a transparent polymer sheet which has been coated on one sidewith a transparent electrically conducting layer. The sheet acts as atransparent electrode upon which the remainder of the device is built,usually as a multi-layer structure.

Another approach (exemplified by the photovoltaic device described in DE19846160), is to fabricate the device on a non-transparent, flexiblepolymer film and then overlay a transparent polymer film upon it, tothereby exclude vapour, oxygen, or dust from the device.

While techniques such as those described above are technicallysuccessful, they are typically not amenable to high volume, low-costmass-production manufacturing, especially in respect of devices whichinteract with light. The cost of manufacturing such devices may,however, be a critical factor in their physical uptake by society.Indeed, in many cases it is purely the cost and complexity ofmanufacturing such devices that has halted their general use andapplication.

A range of electrical devices are currently manufactured in flexible,low-profile formats. This includes batteries, capacitors, andsuper-capacitors which employ flexible polymeric bases or packagingelements. For example, JP7037559, JP11086807, EP0499005, KR20010029825,JP3034519, and U.S. Pat. No. 5,650,243 describe batteries, capacitors,or super-capacitors which are manufactured by laminating such devicesbetween two or more polymer films. Batteries, capacitors, andsuper-capacitors are generally far less demanding to manufacture thanlight-modulating devices since they do not require optical transparencyin the flexible polymeric components and their layered arrangement istypically much more forgiving of minor variations in the layerthicknesses. Light-modulating devices are notoriously sensitive suchvariations, which often destroy their utility completely. The laminatingpolymers in the abovementioned batteries, capacitors, andsuper-capacitors are therefore primarily incorporated for the purposesof excluding vapour, oxygen, or dust, or for making such devices morerugged.

In a related area, hydrogen (H₂) has long been considered an ideal fuelfor the future. When burned in the presence of oxygen (O₂), hydrogenproduces water (H₂O) as the only waste product. It therefore offers aclean, non-polluting alternative to fossil fuels.

Hydrogen has the added advantage that its reaction with oxygen may bemade to take place in a solid-state device known as a fuel cell, whichharnesses the resulting energy not as heat or pressure, but as anelectrical current. Fuel cells offer greater inherent energeticefficiency than simple combustion of the type employed in, for example,internal combustion engines. A convenient source of hydrogen is thesolar-powered splitting of water into hydrogen (H₂) and oxygen (O₂).

Hydrogen made from water using sunlight prospectively offers anabundant, renewable, clean energy source. However, no practical andeconomic device, or method of manufacture thereof, exists to facilitatethis reaction. The potential of solar-produced hydrogen has,consequently, never been realized.

There is a need for improved water-splitting devices and/or methods forthe improved manufacture thereof which address or at least ameliorateone or more problems inherent in the prior art.

The reference in this specification to any prior publication (orinformation derived from the prior publication), or to any matter whichis known, is not, and should not be taken as an acknowledgment oradmission or any form of suggestion that the prior publication (orinformation derived from the prior publication) or known matter formspart of the common general knowledge in the field of endeavour to whichthis specification relates.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided amethod for manufacturing (i.e. fabricating) water-splitting devices orsolar cells. In a particular form, the method provides a relativelyhigh-volume, low-cost mass-production method. In one example embodiment,the method facilitates simultaneous co-assembly of one or more sub-unitsand two or more polymer films or sheets to form a water-splittingdevice.

According to another aspect, there is provided an improvedwater-splitting device, such as a water-splitting solar cell.

In one example form, there is provided a water-splitting device,including a first electrode for producing oxygen gas and a secondelectrode for producing hydrogen gas from water. The first electrode andthe second electrode are positioned between a first outer polymer layerand a second outer polymer layer. At least one spacer layer ispositioned between the first outer polymer layer and the second outerpolymer layer.

In various further examples: two or more spacer layers are positionedbetween the first outer polymer layer and the second outer polymerlayer; the at least one spacer layer, or at least one further spacerlayer, is positioned between the first electrode and the secondelectrode; and/or the first outer polymer layer forms at least part of achannel for the oxygen gas and the second outer polymer layer forms atleast part of a further channel for the hydrogen gas.

In still further examples: the first outer polymer layer and the secondouter polymer layer are walls of extruded twin-wall sheets provided withribs; at least one twin-wall sheet provided with ribs has a metalcoating layer on at least part of an internal surface; the metal isnickel; a first wall of at least one twin-wall sheet is a conductivepolymer and a second wall of the at least one twin-wall sheet is anon-conductive transparent polymer; and/or the first electrode isprovided within a first twin-wall sheet, and the second electrode isprovided within a second twin-wall sheet.

In one example form, there is provided a water-splitting device,including a water-splitting solar cell positioned between a first gaspermeable layer and a second gas permeable layer, and a first polymerfilm and a second polymer film when joined together encapsulating thefirst gas permeable layer and the second gas permeable layer.

In another example form, there is provided a water-splitting device,including: a water-splitting device, including: a first outer polymerfilm; a second outer polymer film; a solar cell positioned between thefirst outer polymer film and the second outer polymer film; and, atleast one spacer positioned between the first outer polymer film and thesecond outer polymer film.

Optionally, a first gas permeable layer is positioned between the firstouter polymer film and the solar cell, and, a second gas permeable layeris positioned between the second outer polymer film and the solar cell.

In another example form, there is provided a method for manufacturing awater-splitting device, the method including, as a single laminationprocess: positioning a water-splitting solar cell at least partiallywithin a recess provided in a first polymer film; fixing a secondpolymer film to the first polymer film so as to cover thewater-splitting solar cell.

According to yet another aspect, water-splitting devices aremanufactured using a set of readily assembled, robust sub-units whichare then combined in a layered arrangement during the course of apolymer lamination process. Preferably, although not necessarily, atleast one recess is provided within one or more of the laminatingpolymers that is specifically designed to accommodate the assembledsub-units. In a particular example form, the laminating polymers servenot only as a robust packaging device, but are integral to the assemblyprocess itself. In another particular example form, at least one of thelaminating polymers is involved in or otherwise facilitates operation ofthe device.

In one example form, there is provided a method for manufacturing awater-splitting device, the method including: positioning awater-splitting unit at least partially within a recess provided in afirst polymer film; and, fixing an optically transparent polymer film tothe first polymer film so as to cover the water-splitting unit.

In another example form, there is provided a water-splitting device,including: a water-splitting unit positioned at least partially within arecess provided in a first polymer film; and, an optically transparentpolymer film fixed to the first polymer film so as to cover thewater-splitting unit.

In a particular example, the device is formed during a single laminationprocess.

In another example embodiment there is provided a method formanufacturing (i.e. fabricating) a water-splitting device, the methodincluding the step of simultaneously assembling a water-splitting unit(which may be comprised of a plurality of sub-units that have beenpreviously laminated) with a first polymer film at a top of thewater-splitting unit and a second polymer film at a bottom of thewater-splitting unit.

In another example embodiment, there is provided a method for producinga water-splitting device, the method including: depositing a layer ofmetal on at least part of the internal surface(s) of a twin-wall sheet;combining the twin-wall sheet with at least one further twin-wall sheetto provide electrodes in the water-splitting device.

In another example embodiment there is provided a high-volume, low-costmass-production method for manufacturing (i.e. fabricating)water-splitting devices, the method comprising a simultaneousco-assembly of:

-   -   (1) one or more distinct sub-units which, when assembled in a        layered arrangement, cumulatively comprise a water-splitting        unit; and    -   (2) two or more polymer films or sheets, wherein:        -   (i) at least one of the polymer films or sheets is optically            transparent, and        -   (ii) at least one of the polymer films or sheets is embossed            (i.e. impressed) with at least one recess into which the one            or more sub-units at least partially fit;            wherein, one of the polymer films or sheets is laminated or            positioned at the top of the unit and another of the polymer            films or sheets is laminated or positioned at the bottom of            the unit.

In another example embodiment there is provided a water-splittingdevice, including:

-   -   (1) one or more distinct sub-units assembled in a layered        arrangement to form a water-splitting unit; and    -   (2) two or more polymer films or sheets, wherein:        -   (i) at least one of the polymer films or sheets is optically            transparent, and        -   (ii) at least one of the polymer films or sheets is embossed            (i.e. impressed) with at least one recess into which the one            or more sub-units at least partially fit;            wherein, one of the polymer films or sheets is laminated or            positioned at the top of the unit and another of the polymer            films or sheets is laminated or positioned at the bottom of            the unit.

It should be noted that reference to embossing (i.e. impressing) toprovide at least one recess should also be taken as a reference toproviding at least one indentation, depression, cavity or the like.

In a particular example, one or more of the sub-units may be electrodesvia which electrical current can be obtained from or input to thewater-splitting device.

Preferably but not exclusively, the polymer films are flexible orsemi-rigid.

Preferably but not exclusively, the sub-units to be co-assembled, may beseparately optimized, prepared, and fabricated so as to be suitable in awater-splitting device. Preferably but not exclusively, the co-assembledsub-units can be custom-designed to be readily accommodated within thehousing that is provided by the recess(es) within the polymer laminate.

Preferably but not exclusively, the co-assembled sub-units may includeone or more “spacers” (i.e. spacer elements or a “spacer layer”) thatmaintain a suitable separation between other sub-units or componentswhich have been or are to be layered. Examples of such spacers, e.g.forming a spacer layer, include, but are not limited to, ribs, embossedstructures, beads, balls, etc.. In still more specific, but non-limitingexamples, the spacers may be Cellgard PP or PE separator membranes(Celgard LLC), glass bubbles of the type produced by 3M (3M™ GlassBubbles iM30K), or the internal ribs or corrugations of extrudedtwin-wall sheet.

Preferably but not exclusively, the sub-units and polymer films orsheets can be assembled in a high-speed, continuous, web-fed process.

Preferably but not exclusively, the electrode layers within theco-assembled sub-units can have separate electrical connections that mayinvolve conducting wires or tabs which pass between the polymer laminateto the outside.

According to various example aspects: the water-splitting unit iscomprised of two or more sub-units and is at least partially formed aspart of a single lamination process or a previous lamination process;the sub-units are layered films; at least one of the sub-units is anelectrode; and/or at least one of the sub-units is a spacer layer orspacers.

According to an example application there is provided a water-splittingcell that yields hydrogen and oxygen from water when illuminated withsunlight and/or upon the application of a suitable voltage.

The water-splitting solar cell device preferably, but not exclusively,comprises of a co-laminate of multiple transparent polymer barrier filmsand gas-permeable (but not water-permeable) films sandwiching awater-splitting unit, in one example embodiment which has beenco-assembled.

The water-splitting solar cell preferably, but not exclusively, includesa back-contact solar cell.

In an example form, the back-contact dye-sensitized solar cellpreferably, but not exclusively, comprises of a co-laminate of twotransparent polymer films sandwiching a multi-layer co-assembly. Thelatter preferably comprises of, but is not limited to, a co-assembly ofthe following items into a multi-layer structure in which the electrodesdo not touch each other:

-   -   (I) a porous, thin titanium foil electrode upon which a layer of        TiO₂ has been deposited and sintered, whereafter a suitable        light-harvesting dye (such as, but not limited to        tris(2,2′-bipyridyl)ruthenium(II) perchlorate) has been adsorbed        to the TiO₂ layer,    -   (II) a spacer which may comprise of a Cellgard PP or PE        separator membrane (Celgard LLC) or glass bubbles of the type        produced by 3M (3M™ Glass Bubbles iM30K), and    -   (III) a thin titanium foil counter electrode.

The entire assembly is preferably, but not exclusively laminated onthree sides and then back-filled with a suitable solvent containing theI⁻/I₃ ⁻ couple that is needed in dye-sensitized solar cells. The solventmay be, but is not limited to acetonitrile, glutaronitrile,methoxypropionitrile, or valeronitrile. The polymer sheets employed inthe lamination may be, but are not limited to Du Pont Sirlyn,polycarbonate, and/or polyester.

However, in an example form for application in a water-splitting solarcell, the working electrode described in (I) above has been furtherelaborated by coating with a layer of the polymer Nafion containing thecubane water oxidation catalyst. An example process is described inInternational Patent Publication No. WO2008/116254-A1, entitled “WaterOxidation Catalyst” which is incorporated herein by cross-reference.

Alternatively, the working electrode described in (I) above may employthe methodology, catalysts, and dyes employed in the journal paperspublished in AngewandteChemie, International Edition (2008), Volume 47,page 7335 (entitled: “Sustained Water Oxidation Photocatalysis . . . ”),or the Journal of the American Chemical Society (2010), volume 132, page2892 (entitled: “Solar Driven Water Oxidation . . . ”), which areincorporated herein by cross-reference. If necessary, an externalvoltage may be applied to the two electrodes in the assembly. Thecounter electrode in the assembly preferably, but not exclusivelycomprises of the electrode (III) above, or a similar conducting surface,coated with a conducting polymer composite, for example of the typedescribed in the journal paper published in Advanced Materials (2010),Volume 22(15) page 1727 entitled “Conducting Polymer Composite Materialsfor Hydrogen Generation”, which is incorporated herein bycross-reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described solely by wayof non-limiting examples and with reference to the accompanying drawingsin which:

FIG. 1 is a schematic diagram illustrating how a recessed element may beembossed or impressed into polymer sheets or films;

FIG. 2 is a schematic diagram displaying the common elements and generalmethodology of an example embodiment;

FIG. 3 is a schematic diagram of an electrochromic device;

FIG. 4 is a schematic diagram of a back-contact dye-sensitized solarcell ;

FIG. 5 comprises three schematic diagrams (a)-(c) which illustrate amethod for assembling a solid state dye-sensitized solar cell. FIG. 5(a)shows the preparation of the working electrode prior to the cellassembly. FIG. 5(b) shows the preparation of the counter electrode priorto the assembly. FIG. 5(c) shows how the various sub-units are assembledto create the final solid state dye-sensitized solar cell during thelamination process;

FIG. 6 shows two schematic diagrams which illustrate: (a) modificationof the working electrode in a back-contact solar cell (of the typeillustrated in FIG. 4) to incorporate a catalyst that is capable ofoxidizing water to dioxygen, O₂, and (b) the modification of the counterelectrode in such a cell to incorporate a catalyst that is capable ofreducing water to dihydrogen, H₂;

FIG. 7 is a schematic diagram illustrating an example method formanufacture of a water-splitting dye-sensitized solar cell;

FIG. 8 is a schematic illustration of several examples of electricalcontacts that may be used;

FIG. 9 is a schematic illustration of several examples of microfluidicplumbing that may be used to move liquids or gases within the cells;

FIG. 10 provides a schematic illustration of an example corrugated (i.e.twin-wall) plastic sheet before and after coating by electroless nickelplating;

FIG. 11 is a schematic illustration of an electrolysis module comprisingof nickel-plated twin-wall sheet structures;

FIG. 12 is a schematic illustration of an example process by which asealed polymer electrolyser may be manufactured;

FIG. 13 is a schematic illustration of an alternative example of part ofa polymer electrolyser; and

FIG. 14 depicts schematically how to manufacture a twin-wall-type unitincluding a transparent wall for use in solar-driven or solar-assistedwater electrolysis.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

The following modes, given by way of example only, are described inorder to provide a more precise understanding of the subject matter of apreferred embodiment or embodiments. In the figures, incorporated toillustrate features of example embodiments, like reference numerals areused to identify like parts throughout the figures.

EXAMPLE 1 General Method for Implementation

FIG. 1 illustrates a general method by which suitable recesses may beembossed or impressed into polymer films. As shown in 120, a polymerfilm 110 is passed between embossing rollers which contain suitablesurface relief structures or protrusions, to thereby impart, under highpressure and possibly, heat, at least one recess 132, indentation,depression, cavity or the like, on the embossed or impressed polymerfilm 130. If desired for particular applications, a plurality ofrecesses can be provided in polymer film 130. It should be noted thatthe particular geometric shape or profile of the recess can be varied,the particular profile of recess 132 as illustrated is by way of exampleonly.

Features can be provided within or integrated as part of the recess, forexample being formed during the embossing or impressing process. Suchfeatures might include pillars, wells, further recesses, walls,protrusions and/or projections, etc.. The features could be used toassist in holding, retaining or positioning a unit or sub-unit in therecess.

FIG. 2 schematically illustrates a general method of an exampleembodiment. The following items and sub-units are co-laminated bysimultaneously passing between laminating rollers to form lamination170:

-   -   (1) (Layer 1): a transparent polymer film 110 which (optionally)        contains no recesses and therefore has the cross-sectional        profile 111;    -   (2) (Layer 2): a thin electrode 140, having the cross-sectional        profile 141, which may comprise of, but is not limited to:        -   a. a metallic foil, such as a Ti, Pt, Al, or Au foil; or        -   b. a printed conducting layer, such as a conductive,            transparent or non-transparent ELG-class ink manufactured by            NorCote Ltd (USA); or        -   c. a deposited metallic conducting layer, such as a Al, Pt,            or Au layer; or        -   d. a deposited, transparent conducting layer such as an            indium tin oxide (ITO) layer; or        -   e. a printed or deposited conducting layer, such as a            conducting polymer layer;    -   (3) (Layer 3): A spacer layer or spacers 150, which is used to        separate the electrodes 140 and 160 and thereby prevent        short-circuits. Examples of such spacers include, but are not        limited to, ribs, embossed structures, beads, balls, etc.. In        still more specific, but non-limiting examples, the spacer layer        may be a Cellgard PP or PE separator membrane (Celgard LLC) or        glass bubbles of the type produced by 3M (3M™ Glass Bubbles        iM30K);    -   (4) (Layer 4): A thin counter-electrode 160, having the        cross-sectional profile 161, which may be comprised of, but is        not limited to, any of the same materials described in (2)a-e        above;

(5) (Layer 5): A polymer film 130, which has been embossed or impressedto have at least one recess; the polymer film 130 has the exemplarycross-sectional profile 131, in which the electrodes and spacers of(2)-(4) above can be accommodated.

Hence, there is provided a method for manufacturing a light-modulatingelectrical device, such as a water-splitting device. The methodincludes, as a single lamination process, positioning thelight-modulating electrical unit (e.g. formed of sub-units being thinelectrode 140, spacer layer 150, thin counter-electrode 160) at leastpartially within a recess provided in the polymer film 130 (i.e. a firstpolymer film). As part of the single lamination process, the transparentpolymer film 110 (i.e. an optically transparent polymer film) is fixedto the polymer film 130 so as to cover the light-modulating electricalunit.

The upper right-hand detail of FIG. 2 shows a physical method ofcombining each of these layers into a single laminated device orproduct. Each layer would typically be continuously drawn off its ownroll and combined, i.e. laminated into a single laminate 170. The methodof lamination or fixing layers may involve any known method, including:(i) effectively, melting the upper and lower polymer sheets into eachother (that is, by application of a hot-rolled lamination technique), or(ii) effectively gluing the upper and lower polymer sheets to each other(that is, by the application of, and intermediacy of a suitableadhesive; the adhesive may be activated by pressure, heat, light, or anyother suitable method). In the case where an adhesive is used to effectlamination, it is to be understood that all of the techniques describedin this and the other examples provided herein would typically beadapted to include the incorporation of an adhesive coating betweenrelevant polymer films and sub-units involved in the lamination.

Following the lamination process, the final film has the exemplarycross-sectional profile 180. By way of illustration, the cross-sectionalprofile 180 of the final film includes the cross-sectional profiles ofan upper transparent layer 111 below which lies, in the recessedcross-sectional profile 131, an upper electrode 141 separated by spacerlayer 150 from a lower electrode 161. One of the electrodes would be theworking electrode of the light modulating device and the other would bethe counter electrode of the light modulating device.

Optionally, the recessed chamber containing electrode 140, spacer layer150, and counter-electrode 160 may contain a liquid electrolyte that isintroduced into a chamber formed by, or at least partially by, therecess, or is introduced into the recess itself, before, during, or inthe process of lamination.

In various examples, the ordering of the transparent film and theembossed (i.e. impressed) film could be changed, for example theembossed film could be positioned as an upper layer and the transparentfilm could be positioned as a lower layer. Furthermore, either or bothfilms could be embossed to each provide at least one recess. Thus, thelight-modulating electrical unit, such as a water-splitting cell, couldalso at least partially fit into a further recess provided in thetransparent polymer film so that both layers have recesses toaccommodate the electrical unit. Still furthermore, both films could betransparent.

While sealed within the polymer laminate, the upper and lower electrodes140 and 160 are generally arranged so as to be connected electrically toan external electrical circuit by the presence of electrical connectionswithin the laminate that extend to the outside.

Optionally, the recessed chamber may have a tailored profile toincorporate in-built spacer elements to prevent one or more of the upperor lower electrodes from sticking to the laminating polymer films andthereby allowing the movement of liquid electrolyte to that electrode.

Example 2 Fabrication of an Electrochromic Device

This example describes an improved method of fabrication of anelectrochromic device, for example of the type described inInternational Publication No. WO2007002989 entitled “Charge ConductingMedium” which is incorporated herein by cross-reference.

FIG. 3 describes a method for manufacturing an electrochromic device. APVDF membrane 1911 is coated on either side with a conducting layer,such as Ag, Pt, or ITO. The upper conducting layer 1913 is the workingelectrode and the lower conducting layer 1914 is the counter electrode.The upper conducting layer 1913 (working electrode) is then over-printedon the top side with a conducting polymer layer 1912, which may be PPy,PEDOT, or PANI. The lower conducting layer 1914 (counter-electrode) isoverprinted with a different conducting polymer 1915, such as forexample, PEDOT. The resulting sub-assembly is designated 190 in FIG. 3.Sub-assembly 190 is co-assembled with a transparent polymer film 110, ofcross-sectional profile 111, and an embossed polymer film 130, having across-sectional profile 131, and subjected to lamination to producelaminate 170. The resulting film 200 has the exemplary cross-sectionalstructure shown. Film 200 includes a transparent upper polymer film 111sandwiching with a lower, recessed polymer film of cross-sectionalprofile 131, where the recess contains the PVDF membrane 1911 which issandwiched with an upper working electrode 1913 upon which is depositeda conducting polymer layer 1912, and a lower counter-electrode 1914 uponwhich is deposited a second conducting polymer 1915. The upper and lowerelectrodes are capable of being connected to an external circuit by theuse and presence of a variety of types of connectors.

When a moderate voltage (for example 1-2 V) is applied across theelectrodes, the conducting polymers change colour according to:

-   -   PPy: yellow to blue or vice versa    -   PEDOT: blue to sky blue, or vice versa    -   PANI: blue to green, or vice versa.

EXAMPLE 3 Fabrication of a Back-Contact Dye-Sensitized Solar Cell

The top sequence in FIG. 4 depicts a method of pre-treating the workingelectrode in a back-contact dye-sensitized solar cell. The lowerschematic in FIG. 4 depicts a process of assembling a back-contactdye-sensitized solar cell.

Referring to the top sequence in FIG. 4:

A thin, porous titanium foil 140, having cross-section 211 is dip-coatedor printed with a TiO₂ layer as shown in step 214. The TiO₂ on thecoated foil is then sintered by heating at step 215. After sintering,the foil has the cross sectional profile 211, coated with a TiO₂ layer212. The foil is then rolled up at step 216, with spacers placed betweenthe successive layers, to thereby yield the rolled up but separated foil217. This separated foil 217 is placed in a bath 218 containing asolution of a suitable dye such as ruthenium(II) tris(2,2′-bipyridyl)perchlorate and allowed to soak at step 219. After soaking for a periodof time, for example 24 hours, the TiO₂ layer has adsorbed significantquantities of the dye. The foil 217 is then removed from the bath 218,washed, dried, and unrolled to give the working electrode 210, which hasthe cross-sectional structure 191, involving the titanium foil 211coated with the TiO₂ layer 212, upon which a layer of the dye 213 isadsorbed.

Referring to the lower schematic in FIG. 4:

A 5-layer co-assembly of the following is then formed in the sequence(top-to-bottom) given below and laminated as shown in FIG. 4:

-   -   (layer 1): An upper transparent polymer sheet 110 having the        cross-sectional structure 111,    -   (layer 2): An upper working electrode 210, which has the        cross-sectional profile 191 (containing the titanium foil 211,        coated with sintered TiO₂ 212, upon which a layer of dye 213 has        been adsorbed),    -   (layer 3): A spacer layer 150,    -   (layer 4): A lower counter-electrode 220, which comprises of a        virgin titanium foil having cross-section 221,    -   (layer 5): A lower embossed polymer film containing a recess and        of cross-sectional profile 131.

The above co-assembly is laminated to form laminate 170, whilstincluding a liquid electrolyte containing the needed ⁻/I₃ ⁻ couple,thereby yielding a polymer film that has the cross-sectional arrangement230; namely.

-   -   an upper transparent polymer film 111 sandwiching a lower        polymer film 131 which contains an embossed recess into which        the back-contact solar cell fits. The assembled back-contact        solar cell has the structure:        -   an upper electrode 211 upon which has been coated a TiO₂            layer 212, which has itself been coated with a suitable dye            213;        -   a spacer 150 to separate the electrodes and prevent short            circuits;        -   a lower electrode 221, which acts as the counter electrode;        -   a liquid electrolyte inside the embossed recess and about            the spacer elements and electrodes.

Upon illumination with sunlight, the laminated back-contact solar cellyields a voltage between the two electrodes. An external circuitconnected to the two electrodes by connecting elements yields a currentas a result of the influence of sunlight on the back-contact solar cell.

The laminated polymer structure of the solar cell is amenable tohigh-volume, low-cost mass production. The laminated polymer layersprotect the solar cell and lengthen its lifetime.

The laminating polymer films may be, for example, Du Pont Sirlyn,polycarbonate, or a polyester. The liquid in the electrolyte may be, forexample, acetonitrile, glutaronitrile, methoxypropionitrile, orvaleronitrile.

The lamination process may involve three sides of the device beinglaminated first, after which the liquid electrolyte is introduced, withthe fourth side being laminated thereafter.

Alternatively, the liquid electrolyte may be introduced into therecessed cavity immediately prior to lamination, which is so constructedas to trap the liquid electrolyte within the laminated polymer film.

EXAMPLE 4 Fabrication of a Solid-State Dye-Sensitized Solar Cell

This example describes an improvement of the method of fabrication of asolid-state dye-sensitized solar cell, for example of the type describedin the journal paper entitled “Flexible and Compressible Gortex-PEDOTMembrane Electrodes for Solid-State Dye-Sensitized Solar Cells”published in Langmuir (2010), volume 26(3), page 1452, which isincorporated herein by cross-reference.

FIG. 5(a) depicts the preparation of the working electrode sub-unit of asolid-state dye-sensitized solar cell prior to its final assembly. Apolymer sheet 240 coated with a transparent conductive layer, such asindium tin oxide (ITO) or a transparent conductive ink of the ELK-seriesproduced by NorCote, has the cross-sectional profile 241. The sheet isdip-coated or printed with a specially-formulated TiO₂ paste in step300. The paste is then sintered using heat or pressure to yield ananoparticulate TiO₂ coating 2412. The resulting sheet ofcross-sectional profile 242 is then rolled up (at step 310), whilstensuring that a small gap exists between each successive sheet in theroll. The resulting rolled up sheet 320 is then placed into a drum-likecontainer 330 containing a coating solution, where it is, first, coatedby adsorption of a suitable light-harvesting dye, followed byelectrocoating of a PEDOT layer. Step 340 shows the rolled up sheet 320in the drum 330 during this treatment. After completion of step 340, thesheet is removed from the drum, dried, and unrolled. The resulting sheet250, now has the cross-sectional profile 243, which comprises of atransparent polymer sheet with transparent conducting layer 2411, whichis overcoated with, first, a sintered TiO₂ layer 2412, and then, second,with a TiO₂-dye-PEDOT layer 2413.

FIG. 5(b) depicts the preparation of the counter electrode sub-unit of asolid-state dye-sensitized solar cell prior to its final assembly. Thebase substrate 251 is, for example, a

Gortex membrane which has been coated with ca. 10 nm poly(maleicanhydride) using low-power plasma polymerization. The resultingplasma-treated Gortex membrane has the cross-sectional profile 2511. Themembrane is then sputter-coated at step 400 with a layer (ca. 40 nmthick) of gold, titanium, or nickel to reduce the sheet resistance. TheGortex electrode is now designated 252 and has the cross-sectionalprofile 2512. It comprises the original plasma-treated membrane 2513overcoated with a layer of gold, titanium, or nickel 2514. In thefollowing step 410, one side of the membrane 252 is subjected to avapour-phase polymerisation of PEDOT. The final form of the Gortexmembrane 253 has a cross-sectional profile 2515 involving aplasma-treated Gortex base 2513, overcoated with a layer 2514 of gold,titanium, or nickel, overcoated by a layer 2516 of PEDOT.

FIG. 5(c) illustrates the assembly of the final solid-statedye-sensitized solar cell. A 4-layer co-assembly is made and laminatedas follows (in the order top-to-bottom, as shown in FIG. 5(c)):

-   -   (layer 1): An upper transparent polymer sheet 110 having the        cross-sectional structure 111,    -   (layer 2): An upper counter electrode 253, which has the        cross-sectional profile 2515 (containing the original        plasma-treated Gortex base 2513, overcoated with a layer 2514 of        gold, titanium, or nickel, which has been further overcoated        with a layer 2516 of PEDOT),    -   (layer 3): A lower working electrode 250, which has the        cross-sectional profile 243, comprising of a transparent polymer        base coated with a transparent conducting layer 2411, which has        been overcoated with sintered TiO₂ 2412, upon which a layer of        dye and PEDOT 2413 has been deposited.    -   (layer 4): A lower embossed polymer film containing a recess of        cross-sectional profile 131.

Note that there is no spacer between layers 2 and 3 of the assembly.Instead, these layers are compressed together by the lamination process.A key advantage of the process is that the Gortex is highlycompressible, thereby ensuring good electrical contact between layer 2and 3. Preferably, there is no liquid electrolyte present in theassembly, which is fully solid-state.

The final assembly has the cross-sectional profile 450. The assemblycomprises the upper polymer sheet 111 laminated to the lower polymersheet 131. Within the recess in the lower polymer sheet is thesolid-state dye-sensitized solar cell, which comprises of the counterelectrode (plasma-treated Gortex 2513, overcoated with a conductingmetallic layer 2514 and a layer of PEDOT 2516, compressed against theworking electrode, which comprises the transparent conductive sheet2411, overcoated with sintered TiO₂ 2412 and a layer of dye and PEDOT2413).

Upon illumination with sunlight, the laminated solid-state solar cellyields a voltage between the two electrodes.

The laminated polymer structure of the solar cell is amenable tohigh-volume, low-cost mass production. The laminated polymer layersprovide the required compression of the two electrodes. The laminatedpolymer layers also protect the solar cell and lengthen its lifetime.

EXAMPLE 5 Fabrication of a Water-Splitting Solar Cell

This example describes an improvement on methods of fabrication of awater-splitting solar cell, for example of the type described inInternational Publication No. WO2008/116254-A1, entitled “WaterOxidation Catalyst”, which is incorporated herein by cross reference.This example also describes an improvement on the methodology employedfor oxygen generation in the journal papers published inAngewandteChemie, International Edition (2008), Volume 47, page 7335(entitled: “Sustained Water Oxidation Photocatalysis . . . ”), theJournal of the American Chemical Society (2010), volume 132, page 2892(entitled “Solar Driven Water Oxidation . . . ”) and Chemistry andSustainability, Energy and Materials (2010) in press (entitled “A TandemWater-Splitting Device Based on a Bio-Inspired Manganese Catalyst”).This example further describes an improvement on the method employed forhydrogen generation in the journal paper published in Advanced Materials(2010), Volume 22(15) page 1727 entitled “Conducting Polymer CompositeMaterials for Hydrogen Generation”.

FIG. 6(a) depicts the processes which are preferably applied to thesub-units which can be used to form the oxygen-generating workingelectrode of a water-splitting solar cell prior to its assembly. Asshown in process 500, a coated titanium foil 210 of cross-sectionalprofile 191, is overprinted with a thin layer of the DuPont polymerNafion 510, which has incorporated within it a suitable water oxidationcatalyst.

As described in Example 3, the coated titanium foil 210 withcross-sectional profile 191 comprises of a thin, porous titanium foilbase 211 which has been coated with a layer of sintered SiO₂ 212, uponwhich a layer of a suitable light-harvesting dye 213 has been adsorbed.Following the application of the process 500, the coated titanium foil520 now has the cross-sectional profile 530 in which the earlierdeposited layers 212-213 are overcoated with an additional layer ofNafion 510 containing a suitable water-oxidation catalyst. Examples ofsuitable water-oxidation catalysts and their correspondinglight-harvesting dyes, and their methods of incorporation into theNafion, include the bio-inspired manganese-oxo cluster described in thearticle published in AngewandteChemie, International Edition (2008),Volume 47, page 7335 (entitled: “Sustained Water OxidationPhotocatalysis . . . ”) and the dye and catalyst combination describedin the article published in the Journal of the American Chemical Society(2010), volume 132, page 2892 (entitled “Solar Driven Water Oxidation .. . ”), which are incorporated herein by cross-reference. A variety ofother physical arrangements of the working electrodes may be used.

FIG. 6(b) depicts the processes which are preferably applied to thesub-units which can be used to form the hydrogen-generating counterelectrode of a water-splitting solar cell prior to its assembly. Avirgin, thin titanium foil 220, having cross-sectional profile 221, isovercoated with a composite co-polymer 222 comprising of PEDOT and PEG(Polyethylene glycol), for example of the type described in the journalpaper published in Advanced Materials (2010), Volume 22(15) page 1727entitled “Conducting Polymer Composite Materials for HydrogenGeneration”), which is incorporated herein by cross-reference. Theresulting counter electrode 224 now has a layered structure 223,comprising of a layer of PEDOT-PEG 222 overlaying the titanium foil 221.

FIG. 7 depicts the incorporation of a water-splitting solar cell orunit, including for example the above working and counter-electrodes,into a single solar water-splitting device. An 11-layer assembly,although other numbers of layers is possible, is laminated in process170 (FIG. 7). In a particular example, the assembly comprises of thefollowing individual layers (listed sequentially from top-to-bottom)

-   -   (Layer 1): An upper (i.e. first) transparent polymer film 130        containing an embossed or impressed recess as depicted in the        cross-sectional profile 131,    -   (Layer 2): A spacer layer 150 to separate the upper polymer        sheet 130 from the gas permeable membrane 600 which is below        spacer layer 150,    -   (Layer 3): A thin, gas-(oxygen)-permeable, but water impermeable        membrane or layer 600, having the cross-sectional structure 610,    -   (Layer 4): A spacer layer 150 to separate the upper electrode        520 from the gas permeable membrane 600 above upper electrode        520,    -   (Layer 5): The coated titanium foil working electrode 520, which        has been prepared as described in FIG. 6(a) (that is, with the        cross-sectional profile 530, containing the thin porous titanium        foil 211 coated with sintered TiO₂ 212 upon which a layer of dye        213 has been adsorbed, followed by coating with a Nafion layer        510 which contains a suitable water oxidation catalyst). The        working electrode 520 generates oxygen gas from water when it is        operating correctly,    -   (Layer 6): A spacer layer 150 to separate the working electrode        520 and counter electrode 224 and prevent short circuits,    -   (Layer 7): A counter-electrode 224, which comprises of a virgin        titanium foil having cross-section 221 coated with the PEDOT-PEG        composite shown in FIG. 6(b). The counter-electrode generates        hydrogen when operating correctly,    -   (Layer 8): A spacer layer 150 to separate the counter electrode        224 from the gas permeable membrane 600 that lies below        counter-electrode 224,    -   (Layer 9): A thin gas-(hydrogen)-permeable, but water        impermeable membrane or layer 600, having the cross-sectional        structure 610,    -   (Layer 10): A spacer layer 150 to separate the bottom polymer        film 130 from the gas permeable membrane 600 which is above        spacer layer 150,    -   (Layer 11): A lower (i.e. second) polymer film 130 containing an        embossed or impressed recess as depicted in the cross-sectional        profile 131.

The above-mentioned co-assembly is laminated to produce laminate 170(FIG. 7), whilst including water as an electrolyte into the centralmicrofluidic cavity 720. Preferably a conduit is included in themicrofluidic plumbing of the resulting laminate that allows a continuousflow of water to be fed into the water-splitting device. Preferably, thewater electrolyte within the device is maintained under suitablepressure to halt the formation of bubbles of oxygen (at the workingelectrode) and hydrogen (at the counter electrode) during the operationof the water-splitting device. While bubbles would ideally be preventedfrom forming, gases will, nevertheless, be continuously generated andsaturate the water electrolyte as dissolved species.

The resulting laminate 170 has the exemplary cross-sectional structure700, which contains three distinct microfluidic cavities:

-   -   cavity 720, into which water is continuously (or potentially        periodically) added as an electrolyte via a suitable conduit in        the microfluidic plumbing of the laminate,    -   cavity 710, into which oxygen gas that is generated at the upper        working electrode 520 during water-splitting is transported        (through membrane 610) and carried away. Preferably a conduit is        included in the microfluidic plumbing of the laminate that        allows a continuous flow of oxygen gas to be fed out of the        device via the cavity 710, to thereby collect the oxygen that is        produced. (The upper working electrode 520 comprises of layers        211, 212, 213, and 510).    -   cavity 730, into which hydrogen gas that is generated at the        lower counter electrode 224 during water-splitting is        transported (through membrane 610) and carried away. Preferably        a conduit is included in the microfluidic plumbing of the        laminate that allows a continuous flow of hydrogen gas to be fed        out of the device, via the cavity 730, to thereby collect the        hydrogen that is produced. (The lower counter electrode 224        comprises of the layers 221 and 222).

The cross-sectional profile 700 of the device, thus manufactured,therefore includes:

-   -   (i) an upper transparent, recessed polymer film 131 and a lower,        counter-recessed polymer film 131 which sandwich two, recessed        gas-permeable membranes, between which a water-splitting solar        cell has been included, for example a water-splitting back        contact solar cell. Suitable spacer layers or spacers separate        each of these components. Examples of such spacer layers or        spacers include, but are not limited to, ribs, embossed        structures, beads, balls, etc.. In still more specific, but        non-limiting examples, the spacers may be Cellgard PP or PE        separator membranes (Celgard LLC) or glass bubbles of the type        produced by 3M (3M™ Glass Bubbles iM30K).The cross-sectional        structure of the included water-splitting back-contact solar        cell is (from to-to-bottom in sequence):        -   an upper spacer layer to separate the water-splitting            back-contact solar cell from the remaining components.        -   an upper, working electrode 520, which generates oxygen gas            from the water electrolyte when operating correctly. The            working electrode 520 comprises a porous Titanium foil 211            upon which has been coated a TiO₂ layer 212, which has            itself been coated with a suitable dye 213 and then with a            Nafion layer 510 containing a suitable water oxidation            catalyst, as shown in FIG. 6(a).        -   a spacer layer 150 to separate the working and counter            electrodes of the water-splitting back-contact solar cell            and prevent short circuits.        -   a lower, counter electrode 224, which acts as the counter            electrode and generates hydrogen gas from the water            electrolyte when operating correctly. The electrode 224            comprises a thin titanium foil 221, overcoated with a            PEDOT-PEG composite 222 as shown in FIG. 6(b).        -   a lower spacer layer to separate the water-splitting            back-contact solar cell from the remaining components.    -   (ii) the liquid electrolyte water inside the recess(es) or        cavity 720, which is surrounded by gas permeable membranes 610,        above and below.

It should be noted that both upper (i.e. first) and lower (i.e. second)polymer films 130 could be transparent. Furthermore, according toanother example, only one of the upper (i.e. first) or lower (i.e.second) polymer films 130 could be provided with a recess, while theother polymer film is not recessed.

EXAMPLE 6 Types of Electrical Contacts

There is a need for external electrical connections that connect to theelectrodes inside the laminate. FIG. 8 depicts examples of suitableexternal electrical contacts. The upper schematic in FIG. 8 depicts aninsert that may be employed to provide an external electrical contactwith the lower electrode in various example devices. The middleschematic of FIG. 8 depicts an insert that may be employed to provide anexternal electrical contact with the upper electrode in various exampledevices. These electrodes, that can be provided as inserts, can have apartial surface area that is conducting and a partial surface area thatis insulating.

Referring to the upper schematic in FIG. 8:

In cases where the lower electrode in the device to be incorporated inthe laminate is an exposed metal or conducting material (such as isdescribed in Example 1), an insert 810 can be included in the assemblyand lamination process as shown in 830 and 840 (where 800 is the upperpolymer film of the laminate and 820 is the lower polymer film). Theinsert 810 may comprise of a thin metal or conductive material, wherethe conducting surface is exposed 811 on each end, with other areas 812made insulating by coating with an insulator. When included in anassembly of the type described in Example 1 as shown in the upperschematic in FIG. 8, the lower exposed, conducting area 811 willnecessarily be pressed into close contact with the lower, exposed,conducting electrode of the device incorporated within the recess 820 ofthe lower plastic sheet. The upper exposed area 811 (marked “L”) ofinsert 810 would however lie outside of the laminate. Thus, an externalelectrical contact would be established between the upper exposed,conducting area 850 (marked “L”) and the lower electrode of the deviceincorporated in the recess 830 of the lower polymer sheet. Theinsulating areas 812 will ensure that this electrical connection willnot short-circuit with the upper electrode of the device incorporated inthe recess 830.

Referring to the middle schematic in FIG. 8:

In cases where the upper electrode in the device to be incorporated inthe laminate is an exposed metal or conducting material (such as isdescribed in Example 1), an insert 860 can be included in the assemblyand lamination process as shown in 870 and 880 (where 800 is the upperpolymer film of the laminate and 820 is the lower polymer film). Theinsert 860 may comprise of a thin metal or conductive material, wherethe conducting surface is exposed 861 on each end, with other areas 862made insulating by coating with an insulator. When included in anassembly of the type described in Example 1 as shown in the middleschematic in FIG. 8, the right-hand exposed, conducting area 861 willnecessarily be pressed into close contact with the upper, exposed,conducting electrode of the device incorporated within the recess 820 ofthe lower plastic sheet. The left-hand exposed area 861 (marked “U”) ofinsert 860 would however lie outside of the laminate. Thus, an externalelectrical contact would be established between the outer exposed,conducting area 890 (marked “U”) and the upper electrode of the deviceincorporated in the recess 830 of the lower polymer sheet. Theinsulating areas 862 will ensure that this electrical connection willnot short-circuit with the lower electrode of the device incorporated inthe recess 830.

Referring to both the upper and middle schematic of FIG. 8:

In cases where one or more electrodes of the device to be incorporatedin recess 820 do not have conductive surfaces directly exposed duringlamination, the inserts 810 or 860 may be physically attached to theelectrodes prior to the assembly being laminated. This attachment wouldinvolve a method that creates direct electrical connectivity between theconduction layer of the electrode and the inner exposed conductionsurface 811 or 861 of the insert 810 or 860, respectively. For example,the insert may be glued to the electrically conductive surface of theelectrode using a conducting glue. Alternatively, the insert may besoldered to the electrically conductive surface of the electrode. Afterconnecting the insert, the assembly may proceed as normal. The resultingdevice will have an exposed electrical contact 850 or 890 at one side ofthe laminate.

For convenience and to avoid electrical short circuits, the upperelectrode contact would typically be inserted at the opposite end of thedevice to that of the lower electrode contact. The two inserts may, forexample, be included at the top and bottom of the device, or on the leftand right of the device.

The lower schematic in FIG. 8 illustrates methods of connecting theexternal electrical contacts of cells constructed in this way. Cells maybe arranged and connected in a “head-to-toe” arrangement (seriesconnection) as shown in the left-hand schematic at the bottom of FIG. 8.Alternatively, cells may be arranged in a “side-by-side” arrangement(parallel connection).

EXAMPLE 7 Types of Plumbing for Liquid and Gas Movement Within Cells

Another feature which can be included in example embodiments of awater-splitting device is microfluidic plumbing for the purposes ofmoving gases or liquids in the cells. FIG. 9 illustrates examples ofmicrofluidic plumbing which can be created by embossing or impressingthe overlying or underlying polymer sheet(s) and/or attaching externalconnecting hoses, pipes, tubes, nozzles or the like.

The upper schematic in FIG. 9 illustrates microfluidic plumbing thatwould typically be suitable for transmission of both liquids or gases. Arecess 910 that has been embossed or impressed within a laminatingpolymer sheet is connected to the outside of the laminate by aconnecting hose 900. The hose would typically be separately moulded andthen later affixed within a hole in the embossed recess, as shown. Thehose may be glued into the hole, or mechanically jammed into the hole.

The lower schematic in FIG. 9 illustrates microfluidic plumbing whichincorporates embossed or impressed spacer units 920 or 930, that wouldtypically be suitable for transmission of gases only. Plumbing of thissort may be created by the use of a carefully tailored embossing dyethat incorporates surface relief features capable of creating spacerunits like 920 or 930. A connecting hose 940 connects the outside of thelaminate with the plumbing. The hose would typically be separatelymoulded and then later affixed within a hole in the embossed recess, asshown. The hose may be glued into the hole, or mechanically jammed intothe hole.

EXAMPLE 8 Further Embodiment of a Water-Splitting Device

This example describes a further embodiment of a water-splitting solarcell. In this example the fabrication process and resulting device isdifferent to that illustrated in FIG. 7. In this example use is made ofan extruded twin-wall plastic sheet having a series of vertical spacersor ribs(herein referred to as “twin-wall sheet”) that are periodicallyspaced along and between the twin-walls to keep them separated.

The sheet can be made from a polymer, preferably polypropylene, althougha range of other plastics can be used. In specific examples, the sheetcan be made from a polypropylene co-polymer or high densitypolyethylene. It is also possible, and perhaps desirable in thisapplication, to make the different walls of the sheet from differentmaterials, for example a conductive polymer, a non-conductive polymer, atransparent polymer, an opaque polymer, or combinations thereof. In aparticular non-limiting example, the extruded twin-wall plastic sheetcan be Corflute® or Fluteboard® twin-wall sheet manufactured by CorexPlastics (Australia) Pty Ltd, or similar products sold by othermanufacturers and sometimes termed corrugated plastic.

The twin-wall sheet can be used as a frame or skeleton in an additionalembodiment of the water splitting device. The ribs or corrugations ofthe twin-wall sheet provide the spacers (i.e. spacer layer). In thisexample, the following steps can be used to manufacture the watersplitting device.

-   -   (1) Manufacturing or obtaining the twin-wall sheet.    -   (2) Treating the twin-wall sheet with a coating process, such as        dip-coating, which applies a thin layer of conducting metal, for        example and preferably nickel, deposited on at least part of the        internal (inside) surface(s) of the twin-wall sheet.    -   (3) The deposited metal layer, e.g. nickel layer, is used as an        electrode in water electrolysis (especially alkaline water        electrolysis). The resulting oxygen or hydrogen gas bubbles are        guided and confined by the internal cavities of the twin-wall        sheet (from where the gas can be collected). A variety of        suitable catalysts can also be utilised, for example LiCo₂O₄,        coated onto a suitable deposited metallically-conductive layer.    -   (4) By combining two or more twin-wall sheets as above, as        opposing or co-electrodes in a planar electrolyzer, stacked        twin-wall sheets can be used as a water-splitting device.

In a further variation, the twin-wall sheet can be extruded duringmanufacture with two different polymers as the walls—one wall being a“conductive” polymer, on which a metal such as nickel is readily coated,and the other wall being a “non-conductive” transparent polymer on whichmetal such as nickel does not plate. This results in a unit having onelayer (i.e. outer polymer layer or wall) transparent, and the otherlayer (i.e. other outer polymer layer or wall) an electrode. Such a unitcan be used as a solar cell, where light enters through the transparentlayer and falls on the internal electrode surface. The gases generatedare still collected by the internal channels of the twin-wall sheet.

Thus, in the twin-wall sheet example water-splitting device, the, frameor skeleton of the device, including the ribs or separators acting asspacers, is manufactured first and the internal components/layers arethen added or incorporated. Thus, the order of manufacture of thewater-splitting device may be varied and the order of application of thelayers in the device may also be varied. The electrodes may be producedon a pre-assembled frame or skeleton.

This example generally provides a water-splitting device including afirst electrode for producing oxygen gas and a second electrode forproducing hydrogen gas from water. The first electrode and the secondelectrode are positioned between a first outer polymer layer (i.e. wall)of a first twin-wall sheet, and a second outer polymer layer (i.e. wall)of a second twin-wall sheet that are stacked together. At least onespacer layer, that is the series of ribs from either the first twin-wallsheet or the second twin-wall sheet is positioned between the firstouter polymer layer and the second outer polymer layer.

In this example, it can also be said that there are two or more spacerlayers (the series of ribs from the first twin-wall sheet and the seriesof ribs from the second twin-wall sheet) positioned between the firstouter polymer layer and the second outer polymer layer. The first outerpolymer layer (i.e. wall) thus forms at least part of a channel for theoxygen gas and the second outer polymer layer (i.e. wall) thus forms atleast part of a further channel for the hydrogen gas.

The produced water-splitting device still has the form of a multi-layerdevice for water splitting which has plastic or polymer outer wallsenclosing electrodes and spacers, that is at least one spacer layer.

According to a particular non-limiting form, a further examplewater-splitting device utilising twin-wall sheets is now described inmore detail by way of illustration.

An example of twin-wall sheet, so-called “conductive” Corflute® sheet(M/F 4.0 mm 750 gsm) manufactured by Corex Plastics (Australia) Pty Ltd,was purchased. According the specifications provided by themanufacturer, the twin-wall sheet comprised of polypropylene doped withca. 30% by weight of carbon black. The presence of the carbon blackmakes the polymer weakly conductive. “Conductive” corrugated plastics ofthis type are used as packaging in applications where static electricityneeds to be minimized (e.g. during the transportation of electricalcomponents). Several non-conductive Corflute® sheets of similardimensions were also purchased.

Corflute® sheets are an example of a corrugated plastic comprising oftwo layers of polymer held apart and separated by a succession ofregularly-spaced plastic ribs lying orthogonal to the two outer plasticlayers (that is, “twin-wall sheet”). The ribs create channels that runthe length of material. FIG. 10 provides a schematic illustration of the“conductive” (M/F 4.0 mm 750 gsm) Corflute® sheet referred to above. Ascan be seen, in this exemplar material, the outer layers of plastic areseparated by ca. 3 mm, with the ribs between the layers periodicallyspaced ca. 4 mm apart. The result is that this material has ahoneycombed structure, comprising of a linear succession of parallelchannels, each of which have dimensions 3 mm x 4 mm and which run thelength of the structure.

The Corflute® sheet samples were subjected to a dip-coating process usedto carry out electroless nickel plating. Electroless nickel plating isknown to be used to coat ABS (acrylonitrile butadiene styrene)polymerswith a thin layer of nickel upon which a variety of metallic finishesmay then be electrolytically deposited. The nickel layer provides ahighly conductive surface for the subsequent electrolytic depositionstep. The key advantages of electroless nickel plating include: (1) Noelectrical current is required for the plating—it is electroless,meaning that nickel plates purely as a result of being dipped in theplating solution (—the thickness of the plated layer depends on the diptime and the strength of the plating solution), and (2) the nickelplates extremely uniformly over the item, including for irregularsurface structures.

The electroless nickel process used in the case of the Corflute® sheetexamples referred to above comprised of two dip-coating procedures, thefirst of which involved a so-called “palladium strike”, in whichmicrocrystallites of palladium are first deposited on the item surfaceto serve as crystallization sites for the subsequent nickel deposition,followed by dip-coating in an electroless nickel bath.

Tests indicated that the standard, “non-conductive” Corflute® sheetsamples were entirely resistant to nickel coating using the aboveprocedure. No nickel could be deposited on their surfaces using theabove technique. However, the “conductive” Corflute® sheet samples werereadily coated with a layer of nickel using this example procedure.Moreover, the layer thickness could be readily varied by changing thetime during which the Corflute® sheet was dipped—the relationship wasroughly 1 μm thickness for every 1 minute of dipping time using theelectroless nickel coating solution employed by A Class Metal Finishers.

It has hitherto been common-wisdom that polymers like polypropylene,which contain no readily accessible functional groups on their surface,cannot be coated with nickel or other metals using electroless plating.However, surprisingly it has been identified that such polymers may berendered “plate-able” using electroless techniques, by the incorporationof substantial quantities of carbon black or other conductiveparticulates within them.

Also of relevance, is the fact that nickel serves as theindustry-standard electrode material for both the cathode and anode inalkaline water electrolyzers. In commercial electrolyzers of this type,nickel sheets or nickel-coated stainless steel are widely used. In thelatter case, the stainless steel needs to be of a type that withstandsthe highly alkaline environment (typically 3-6 M KOH) that is used inthis class of electrolyser.

It is also relevant that polypropylene, which is typically used as thepolymer in twin-wall sheets, such as Corflute® sheets and othercorrugated plastics, is extremely resistant to degradation in stronglyalkaline solutions. It is known in the art that polypropylene isunaffected by extreme, basic, environmental conditions.

Thus, the combination of nickel-coated polypropylene twin-wall sheets,for example nickel coating of the “conductive” Corflute® sheetsdescribed above, opens the possibility of a “plastic”-based electrolysermodule for application in alkaline water electrolysis.

To assess this possibility, nickel-coated Corflute® sheets were testedas the cathode and anode in alkaline water electrolysis. Two sheets ofnickel-coated Corflute® sheet were placed adjacent to each other, butnot in electrical contact, within a glass bath containing 1 M aqueousKOH solution. The twin-wall sheets were oriented so that the internalchannels ran from top-to-bottom (not from side-to-side).

FIG. 11 depicts the experimental arrangement in this proof-of-conceptdevice. Two nickel-coated Corflute® sheets 1000 were prepared and facedtoward each other as shown in FIG. 11. A series of small holes 1100 weredrilled into the facing sides on each twin-wall sheet 1000. The holesare required to allow for movement of the electrolyte solution betweenthe two twin-wall sheet electrodes. A spacer 1200, which comprised inone embodiment, of a gasket-like insulating polypropylene was introducedbetween the two twin-wall sheets. The spacer 1200 separated the twosheets 1000 and prevented a short circuit due to electrical contactbetween the nickel coatings on the two sheets 1000. The spacer 1200 washot welded to the two sheets 1000, enclosing and sealing the spacebetween the two sheets 1000. The entire assembly 1300 was then immersedup to the level shown at 1400,in an aqueous solution containing 0.1-3 MKOH.

The twin-wall sheets 1000 in the assembly 1300 were separately connectedto a potentiometer, with one sheet polarized as the anode and the othersheet as the cathode. A voltage of 2-4 V was then applied between thetwo sheets. Upon the application of a voltage within this range, bubblesof hydrogen could be seen to immediately start forming on the cathode;bubbles of oxygen formed on the anode. The bubbles continued as long asthe voltage was applied, over a period of 24 hours, without anysignificant fall-off in the rate of gas generation or current measured(under a constant applied potential). When the voltage was turned off,gas generation ceased immediately. When it was then turned on again, gasgeneration immediately re-commenced.

The bubbles referred to above were readily observable on the outside ofthe nickel-coated twin-wall sheets 1000. However, when viewed fromabove, it could also be seen that a substantial volume of bubbles wereformed within the inner channels of the twin-wall sheet electrodes,which have a substantially higher geometric and electrochemical areathan the outside. These bubbles rose to the surface of the electrolytesolution, guided by the channels. At the top of each channel a layer offroth-like bubbles was seen to form. A gas-permeable, butwater-impermeable Nafion membrane 1500 was stretched over the top of theinternal channels and attached to thereby allow separation of the gasesin the bubbles from the aqueous electrolyte solution within the innerchannels of the twin-wall sheets. The resulting assembly 1310 generatedgases which permeated through the membrane 1500.

Thus, the internal channels of the twin-wall sheets 1000 provided spacerlayers within which gas bubbles could form and be separated. Separateexperiments also indicated that the internal channels of the twin-wallsheet samples could be moderately pressurized; that is, gases couldpotentially also be formed and collected under moderate pressures when atwin-wall sheet-like polymer structure was used as the electrolyserunit.

Thus, there is provided a first electrode for producing oxygen gas, anda second electrode for producing hydrogen gas from water. The firstelectrode and the second electrode are positioned between a first outerpolymer layer, i.e. an outer wall of one of the twin-wall sheets, and asecond outer polymer layer, i.e. an outer wall of the other twin-wallsheet. At least one spacer layer, provided by the ribs of either of thetwin-wall sheets, is positioned between the first outer polymer layerand the second outer polymer layer.

To further optimize the performance of the twin-wall sheet electrodes,the nickel coatings may themselves be electro-coated or coated in otherways, with a variety of catalytic materials, or materials which improvedthe catalytic performance under similar or less alkaline conditions.Examples of such materials are described in a study entitled:“Pre-Investigation of Water Electrolysis”, Report PSO-F&U 2006-1-6287,issued by the Department of Chemistry, Technical University of Denmark(KI/DTU), the Fuel Cells and Solid State Chemistry Department, RiseNational Laboratory, Technical University of Denmark, and DONG Energy.The investigation constituted the main part of the project 6287“Pre-investigation of Electrolysis” funded by the Danish Public ServiceObligation programme (PSO) under Energinet.dk. Since the issuance ofthat report, a variety of other, efficient catalysts have beendiscovered, including a range of catalysts that mimic the active sitesin the hydrogenase and the photosystem II photosynthetic enzymes.

On the basis of these results, several forms of polymer and/or alkalineelectrolysers are possible. FIG. 12 displays a schematic of one suchelectrolyser. An assembly 1300 has a gas permeable membrane 1500 sealedover the top of the twin-wall sheet channels. Atop the membrane, twopolymer gas collection plumbing units 1600 are affixed and sealed. Onegas collection plumbing unit 1600 is affixed in such a way that itexclusively collects the gases arising from the cathode (hydrogen) 1700.The other gas collection plumbing unit is affixed in such a way as toexclusively collect gases arising from the anode (oxygen) 1700. Whenimmersed in an aqueous electrolyte solution, the resulting unit 1320generates hydrogen and oxygen gas upon the application of a suitablevoltage. The gases are collected separately.

The assembly 1320 can be turned into a sealed cell by attaching andsealing a water and gas impermeable polymer base 1900 to the bottom ofthe assembly 1320. If a water inlet 1800 is then also introduced asshown, then the resulting unit is a sealed cell 2000 into which watermay be introduced (through the inlet 1800) and out of which hydrogen andoxygen are collected at cathode and anode 1700. The cell 2000 does notneed to be immersed into the electrolyte solution. Instead, it containsthe electrolyte solution wholly within itself.

Sealed cells 2000 of this type are modular units which can be connectedto each other in series or parallel in order to generate quantities ofhydrogen and oxygen. Moreover, sealed cells may be pressurized togenerate the gases under moderate pressures.

A variation on the sealed cell 2000 of FIG. 12 is illustrated as partialcell 2090 in FIG. 13. A plastic spacer 2010 includes a single sheet ofpolymer with ribs 2020 pointing outward on both sides. Spacer 2010 canalso have small holes down the length of the polymer sheet. Two metallicfilms 2030 are pressed up against the ribs 2020 on each side of spacer2010. The films 2030 can be made of, for example nickel, but othermetals or conductors are possible. Also, films 2030 may be a materialcoated with a metal such as nickel. Furthermore, different metals orconducting materials could be used for each film 2030. The films 2030act as the electrodes. The films 2030 may be decorated with surfacecoatings containing other catalysts. The films 2030 may have tiny holesin them to allow for water to move between them. Outer polymer housings2040, which can also be ribbed on one side, are used to sandwich thewhole arrangement into a sealed cell. Gas collection plumbing and waterinlet valves can be provided similar to those depicted in FIG. 12.

A further variation of a modular water electrolyser based on a twin-wallsheet-like or corrugated plastic structure, involves the manufacture ofa solar-driven or solar assisted water electrolysis device of this type.

FIG. 14 shows how a twin-wall sheet having utility in solar-driven orsolar-assisted water splitting may be manufactured. Twin-wall sheets aretypically manufactured by extruding a sheet of polypropylene containingthe upright ribs (2200) closely adjacent to a separate polypropylenesheet 2100 extruded directly above it. The two component sheets 2100 and2200 are then layered upon each other immediately after they have exitedthe extruder and while they are still hot. In the process of cooling,the two component sheets 2100 and 2200 are welded to each other, therebygenerating the characteristic double-layer or twin-wall structure.Because the two layers are extruded separately, it is possible to usedifferent polymer feed stocks in each layer or component sheet. FIG. 14depicts the example situation where a “conductive” polypropylene(containing 30% carbon black) is used to extrude the ribbed sheet 2200,while “non-conductive”, transparent polypropylene is used to extrude theupper, non-ribbed sheet 2100. When component sheets 2100 and 2200 arecombined to form the twin-wall sheet 2300, the upper surface 2100 ofsheet 2300 will be transparent (and “non-conductive”), while the lowersurface and the ribs 2200 will be black (and conductive).

Thus, twin-wall sheet 2300 includes one surface transparent to light.When the twin-wall sheet 2300 is subjected to electroless nickelplating, only the “conductive”, lower layer and ribs 2200 will be platedwith nickel (or other selected metal or conductor). The upper,transparent component sheet 2100 will remain uncoated and transparent. Alight-driven or light-assisted catalyst may then be selectively affixedto the nickel layer of the lower, ribbed “conductive” surface, leavingthe transparent surface untouched. When the aqueous electrolyte isintroduced into the channels of the resulting twin-wall unit, thecatalyst may act under the influence of sunlight to facilitate thewater-splitting transformation. Using such a twin-wall unit in a sealedcell of the type 2000, may yield a light-driven or light-assistedelectrolyzer.

A “hybrid” electrolyser may be constructed by, for example, combining asolar-driven anode twin-wall unit and an electrically-driven anodetwin-wall unit with a common mutual cathode twin-wall unit. Such anelectrolyzer will be capable of generating gases for 24 hours ofoperation, with the light-driven anode operating with the assistance ofsunlight during the day and the electrically-driven anode operating atnight. The mutual cathode can operate at all hours.

Various other combinations of electrodes can be envisioned.

The key advantage of using twin-wall sheets or corrugated plastics, inthe manufacture of electrolyzers, is their low cost and ready commercialavailability. Moreover, the polymeric structures of these units can bereadily modified by hot welding, melting and re-solidifying.

Optional embodiments of the present invention may also be said tobroadly consist in the parts, elements and features referred to orindicated herein, individually or collectively, in any or allcombinations of two or more of the parts, elements or features, andwherein specific integers are mentioned herein which have knownequivalents in the art to which the invention relates, such knownequivalents are deemed to be incorporated herein as if individually setforth.

It will be appreciated that the embodiments described above are intendedonly to serve as examples, and that many other embodiments are possiblewith the spirit and the scope of the present invention.

1.-21. (canceled).
 22. A water splitting device comprising at least onecathode and at least one anode, wherein at least one liquid-permeableand gas-permeable spacer layer is positioned between the at least onecathode and the at least one anode, and wherein the water splittingdevice is arranged so that liquid electrolytes can permeate through theat least one liquid-permeable and gas-permeable spacer layer and thus bein fluid communication with both the at least one cathode and the atleast one anode.
 23. The water splitting device according to claim 22,wherein the at least one spacer layer extends substantially across asurface of either or both of the at least one cathode and the at leastone anode.
 24. The water splitting device according to claim 22, whereinthe at least one spacer layer separates the at least one anode and theat least one cathode and permits a flow of the liquid electrolytestherebetween.
 25. The water splitting device according to claim 22,wherein the at least one cathode and the at least one anode are formedfrom one or more flexible materials.
 26. The water splitting deviceaccording to claim 22, wherein at least one proton exchange membrane ispositioned between the at least one cathode and the at least one anode,and wherein spacer layers are positioned between the at least one protonexchange membrane and the at least one cathode and the at least oneanode.
 27. The water splitting device according to claim 22, wherein atleast one anion exchange membrane is positioned between the at least onecathode and the at least one anode, and wherein spacer layers arepositioned between the at least one anion exchange membrane and the atleast one cathode and the at least one anode.
 28. The water splittingdevice according to claim 22, wherein the at least one spacer layer isin the form of ribs, embossed structures, nets, woven fabric material,non-woven fabric material, beads, balls or separator membranes.
 29. Thewater splitting device according claim 22, wherein there are at leasttwo cathodes and at least two anodes arranged in at least twocathode-anode pairs, and wherein a spacer layer of the at least onespacer layer is positioned between a cathode and an anode of two or moreof the at least two cathode-anode pairs.
 30. The water splitting deviceaccording to claim 22, wherein the at least one cathode and the at leastone anode are positioned between a first outer polymer layer and asecond outer polymer layer.
 31. The water splitting device according toclaim 30, wherein a first gas permeable layer is positioned between thefirst outer polymer layer and the at least one cathode, and a second gaspermeable layer is positioned between the second outer polymer layer andthe second electrode.
 32. The water splitting device according to claim30, wherein the first outer polymer layer and the second outer polymerlayer are flexible.
 33. The water splitting device according to claim30, wherein the first outer polymer layer or the second outer polymerlayer is formed of a conductive polymer on which a metal is deposited.34. The water splitting device according to claim 30, wherein either oneor both of the first outer polymer layer and the second outer polymerlayer are transparent.
 35. The water splitting device according to claim34, wherein the at least one cathode and the at least one anode form atleast part of a solar cell.
 36. The water splitting device according toclaim 35, wherein the first outer polymer layer and/or the second outerpolymer layer include a recess into which the solar cell at leastpartially fits.
 37. The water splitting device according to claim 34,wherein either one or both of the at least one cathode and the at leastone anode include a titanium foil or coated titanium film.
 38. The watersplitting device according to claim 34, wherein either one or both ofthe at least one cathode and the at least one anode include a coveringlayer which includes a water oxidation catalyst.
 39. A water splittingdevice comprising: at least one cathode and at least one anode arrangedin at least one cathode-anode pair; at least one electrolyte layerspacer positioned in an electrolyte layer of the at least onecathode-anode pair, wherein the at least one electrolyte layer spacerseparates the at least one anode and the at least one cathode andpermits a flow of liquid electrolytes therebetween; at least one gaspermeable membrane and at least one gas layer spacer, wherein the atleast one gas layer spacer is positioned outside the electrolyte layerand adjacent the at least one gas permeable membrane, and wherein thewater splitting device is arranged so that the liquid electrolytes canpermeate through the at least one electrolyte layer spacer and thus bein fluid communication with both the at least one cathode and the atleast one anode.
 40. The water splitting device according to claim 39,wherein there are provided two or more cathode-anode pairs.
 41. A methodfor treating water, comprising applying a voltage between the at leastone cathode and the at least one anode of the water splitting deviceaccording to claim 22 which includes water, thereby splitting at leastsome of the water and producing hydrogen.
 42. The method for treatingwater according to claim 41, including maintaining an electrolyte underconditions to suppress the formation of at least one of oxygen gas andhydrogen gas in the electrolyte.